cold fusion

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A hypothetical form of nuclear fusion occurring without the use of extreme temperature or pressure.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A hypothetical form of nuclear fusion not requiring the usual immensely high temperatures

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun nuclear fusion at or near room temperatures; claims to have discovered it are generally considered to have been mistaken